<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>
        function d(b) {
            if (b === 1) {
                return 1;
            } else {
                return b * d(b - 1);
            }
        }
//         console.log(d(7));//7*6*5*4*3*2
        console.log(d(5));
    </script>
</body>
</html>